Smelting
Iron ores consist of oxygen and iron atoms bonded together into molecules. To convert it to metallic iron it must be smelted or sent through a direct reduction process to remove the oxygen. Oxygen-iron bonds are strong, and to remove the iron from the oxygen, a stronger elemental bond must be presented to attach to the oxygen. Carbon is used because the strength of a carbon-oxygen bond is greater than that of the iron-oxygen bond, at high temperatures. Thus, the iron ore must be powdered and mixed with coke, to be burnt in the smelting process.
However, it is not entirely as simple as that. Carbon monoxide is the primary ingredient of chemically stripping oxygen from iron. Thus, the iron and carbon smelting must be kept at an oxygen deficient (reducing) state to promote burning of carbon to produce CO not CO2.
- Air blast and charcoal (coke): 2 C + O2 → 2 CO.
- Carbon monoxide (CO) is the principal reduction agent.
- Stage One: 3 Fe2O3 + CO → 2 Fe3O4 + CO2
- Stage Two: Fe3O4 + CO → 3 FeO + CO2
- Stage Three: FeO + CO → Fe + CO2
- Limestone calcining: CaCO3 → CaO + CO2
- Lime acting as flux: CaO + SiO2 → CaSiO3
Read more about this topic: Iron Mines